Antenna structure



Jan. 28, 1941. J, GOLDMANN ANTENNA STRUCTURE Filed May 13, .1938 4Sheets-Sheet 2 IN VEN TOR. lf/M GOLD/VA/V/V A TTORNIL'YZ.

Jan. 28, 1941- ,J. GOLDMANN ANTENNA STRUCTURE Filed May 13, 1938 4Sheets-Sheet 3 INVENTOR.

A TTORNEYS.

Jan. 28, 1941. J. GOLDMANN ANTENNA STRUCTURE Filed May 13, 1938 4Sheets-Sheet 4 INVENTOR. JO/ICH/M GOLD/VA/V/V ATTORNEYS.

Patented Jan. 28, 1941 UNITED STATES ANTENNA. STRUCTURE JoachimGoldmann, Berlin-Wilmersdorf, Germany, asslgnor to InternationalTelephone Development Co. Inc., New York, N. Y., a corporation ofDelaware Application May 13, 1938, Serial No. 207,660 6 Claims. (Cl.250-11) The present invention relates to antenna structures andespecially antenna structures comprising at least one dipole element andmeans for feeding such element or deriving energy therefrom. Theinvention is particularly applicable to transmitting systems of the typegenerally known as beacons.

It is an object of the present invention to provide a radiating systemcomprising at least onefed dipole which shall provide a desiredradiation pattern free from distortion. More speciiically it isan objectto provide such a radiating system comprising a dipole and a lead-inarrangement for said dipole which shall include means to isolate thedipole from the lead-in arrangement to prevent distortions introduced bysaid lead-in arrangement and at the same time shall be free fromdistortions introduced by asymmetry of the dipole or of the isolatingmeans used for isolating said dipole.

It is a further object of the invention to provide a dipole and lead-inunit for antenna systems which shall have substantially the radiantpattern of an ideal cylindrical dipole suspended in free space withoutlead-in lines. -In particular it is an object to provide such a dipoleand lead-in structure which shall be readily adjustable. a

It is a further object of the present invention to provide a radiatingsystem for a course beacon including a main radiating dipole fed over ashielded lead-in line disposed along the dipole axis and effectivelyisolated from this lead-in line except for feeding purposes, wherein theeffective electrical shape of the dipole is perfectly symmetrical andasymmetries resulting from the means used to isolate the dipole areeliminated.

It is a further object to provide such a radiating system including inaddition to the main radiating dipole, a plurality of parasiticreflector dipoles controlled by relays, wherein the control wires foractuating the relays are so disposed as to introduce no distortions inthe radiation diagram. It is a further object of the invention toprovide such a radiating system in which one single coaxial line servesboth as the lead-in line for the radiating dipole and also for a controlline to actuate the relays which control the parasitic reflectordipoles.

According to one feature of the .invention, a radiating dipole is centerfed by a line disposed end-on to the dipole along its axis, andextending within the dipole to the center thereof, and the dipole isisolated from such line by resonant circuit structures operatingaccording to the principles set forth in an application filed byFrederick A. Kolster on April 28, 1938, Serial No. 204,735, and assignedto the same assignee as the present application.

According toa further feature of the. present invention, the dipole isso constructed as to form a uniform cylindrical outer surface withinwhich the resonant circuit structure which isolates the dipole from thefeed-line is disposed, so that 10 the outer surface of the dipole issubstantially free from irregularities, discontinuities and asymmetries.According to still another feature of the present invention, the relayswhich control the parasitic dipoles are actuated over lines extendingperpendicular to these parasitic reflector dipoles and to the maindipole. According to still a further feature of the present invention,such perpendicular extending control lines are connected to the coaxialline which feeds the main dipole and the control currents-for the relaysare transmitted over this coaxial line together with the high'freq'uency'currents for feeding the main dipole.

The exact nature of my invention can best'. be understood by referenceto the attached' drawings, in which Fig. 1 represents an elevation of atwo-beam course beacon constructed in accordance with my invention;

Fig. 2 is a sectional elevation of the structure of Fig. 1, taken at thesection plate 2-2, to illustrate the side elevation of one of theparasitic reflector dipoles of the structure of Fig. 1;

Fig. 3 is a sectional elevation of the structure of Fig. 1, taken at thesection plane 33, to illustrate the side elevation of the main radiatingdipole of the structure of Fig. 1;

Fig. 4 is a detailed front elevation of the main radiating dipole ofFig. 1 with part of the housing structure broken away to illustrate theinternal construction:

Fig. 5 is a sectional detail of the lower-limb assembly (generallydesignated as assembly 5 in Fig. 4) of the main radiating dipole;

Fig. 6 is a sectional detail of the upper-limb assembly (generallydesignated as assembly '8 iii' Fig. 4) of the main radiating dipole;

Fig. 7 is a sectional detail of the auxiliary wave controlling assembly(generally designated as assembly I in Fig. 4) of'the main radiatingdipole; I o

Fig. 8 is a sectional detail of the construction at the central junctionof the main radiatin dipole (this central junction being generallydesignated as 8 in Fi 4).

Referring more particularly to Fig. 1, the main radiating dipole I0 isfed at its central junction 8 over coaxial line H, which comprises innerconductor HA and outer conductor or sheath IIB, from the transmitterstation l2, which in the preferred embodiment of my invention is adaptedto provide a continuous supply of ultrashort wave power at a wavelengthof approximately two and one-half meters and at a power level of severalwatts. The dipole l0 whose detailed construction is more clearlyillustrated in Figs. 4, 5, 6, '7 and 8, is supported upon a pole I3,which in the preferred embodiment has a total height of the order offifty or a hundred feet. Attached to the pole I3 is a cross arm l4, nearthe extremities of which the upright arms l5 are adjustably bolted insuch manner that their distance from the pole I3 may be varied. Attachedto the upright arms II are the parasitic reflector dipoles I5 and II,which are essentially similar but differ in respect of the fact thatdipole I6 is normally operative whereas dipole I1 is normallyinoperative.

Each of the parasitic reflector dipoles l6 and I1 comprises two limbs I8having telescopic end portions I9 for adjusting the'length of the limbsto tune the dipole. The two limbs ll of the dipole l6 are jointed attheir center through a relay 20 and the two limbs I8 of the dipole H aresimilarly joined by a relay 2|. The two relays 20 and 2| are preferablyof rugged construction and protected by weatherproof housings. Each ofthese relays is adapted to be actuated by direct current keying signals,the relay 2|] being actuated by signals over the line 22 while the relay2| is actuated by signals over the line 23. The relay 20 has itscontacts arranged so as to normally close the connection between the twolimbs ll! of the dipole l6, and is adapted upon energization to open itscontacts, thus disconnecting the two limbs of this dipole to render thedipole inoperative. Conversely the relay 2| has its contacts arranged sothat normally the .two limbs l8 of the dipole H are disconnected and inresponse to the energization of the relay 2| its contacts are closed tojoin the two limbs of this dipole. Preferably the operatingcharacteristics of the two relays 28 and 2| are so related that uponsimultaneous energization of the two relays, relay 20 will open itscontacts to disable the dipole |.6 before relay 2| closes its contactsto render the dipole effective. Conversely, upon simultaneous cessationof the energization of the two relays relay 2| will preferably open itscontacts to disabledipole before relay 28 recloses its contacts torender dipole l6 again effective.

The lines 22 and 23 extend perpendicularly to. the parasitic reflectordipoles as well as to the main radiating dipole I, so that at all pointsthese lines are transverse to the field of the antenna system.Preferably the lines 22 and 23 are also provided with chokes which maybe housed within the housings of relays 23 and 2|, and if desired otherchokes such as 24 may be inserted in these lines adjacent the mainradiating dipole l0. At the, central junction 8 of dipole Ill, theselines 22 and 23 are connected to the two limbs 5 and 6 of the dipole It,as more clearly shown in Figs. 4 and 8, so that the two lines areconnected in parallel and one wire of each line is conductively joinedto the inner conductor A of the line H, while the other wire. of eachline is con-' ductively joined to the outer conductor or sheath 3 of theline H. The transmitting station I2 is adapted to supply not onlyultra-short wave energy for exciting the main radiating dipole Ill, butalso direct current control, signals for actuating the relays 23 and 2|,these direct current control signals being transmitted over the sameline H which carries the ultra-short wave energy.

The construction of the main radiating dipole It can most readily beseen from Figs. 4, 5, 6, 7 and 8. Referring more particularly to Fig. 4,it

can be seen that the main radiating dipole comprises a lower-limbassembly I and an upper-limb assembly 6, these two assemblies 5 and 5being suitably joined together and supported at the central junction 3,as well as an auxiliary wave controlling assembly I. The lower-limbassembly 5 and the auxiliary wavecontrolling assembly 1 are adjustablyunited by the threaded central sleeve 43 to which both the assemblies 5and I are attached, as more clearly shown in Figs. 5, 7 and 8. Thecentral junction 8 of the main radiating dipole III is protected by awooden housing 3|, shown in Fig. 4 with the front cover removed. Theupper-limb assembly 3 is protected by an insulating tube 32 preferablyof fibrous material impregnated with phenol condensate, this housingtube 32 being supported from the housing 3|, as more clearly shown inFig. 8. A cap 33 protects the top of the housing tube 32 to exclude theentrance of moisture or dirt. A lower housin tube 34 similar to the tube32 protects the lowerlimb assembly '5 and the auxiliary assembly I, thishousing tube 34 being maintained in position by a clamp 35 which bearsagainsta disc closing the lower end of the tube 34, and the tube alsobeing located by a suitable collar at the bottom of housing 3|, as moreclearly shown in Fig. 8.

The structures of assemblies 5, 6 and 1 embody certain of the importantnovel features of the present invention, the exact construction of theseassemblies being clearly illustrated in Figs. 5, 6, '7 and 8. Referringnow more particularly to Fig. 5, it will be seen that the lower-limbassembly 5 illustrated in this figure, comprises a central sleeve 40slidably disposed over the outer conductor B of line H. To this centralsleeve 4|! an enclosing tube 4| is fixed by means of a brass disc 42soldered to central sleeve 48 and screwed to enclosing tube 4|, and bymeans of an insulating disc 43 loosely bearing against central sleeve 48and screwed to enclosing tube 4|. Near the lower end of enclosing tube4| a tubular skirt 44 is adjustably attached to the outer surface of 4|by means of set screws which pass through a spacer ring 43 fixed to thetubular skirt 44. Cooperating with the tubular skirt and with the end ofenclosing tube 4| a condenser cup 43 is threaded on the central sleeve40 so that it may be axially adjusted along this central sleeve to varythe capacity between the cup 48 and the skirt 44 and enclosing tube 4|.A lock nut 41 is provided to maintain the cup 46 in position afteradjustment.

Outside of the upper end of enclosing tube 4| is slidably fitted anexterior tube 49 whose lower end is split and provided with ears 58through which a screw may be passed to clamp the lower end of theexterior tube 43 against the enclosing tube 4|. At the upper end of theexterior tube 49 is soldered a brass disc 5| which is fixed to thesheath 3 of line H by clamping this disc place.

between fitting 52 and nut 53. The fitting 52 which may be made ofbrass, is soldered to the sheath MB of line H and is externally threadedat its upper end to receive the nut 53. On the inside or this fitting 52a plug 54, see Fig. 8, of insulating material such as Isolantite iscemented to form an air-tight and mechanically strong seal with thefitting 52, and a stem 55 extends through the insulating plug 54 and isalso sealed thereto with cement. The inner conductor IIA of line H istubular in form and is soldered over the lower end of stem 55 so thatthe sheath NB, the fitting 52, the plug 54, the stem 55 and the innerconductor A are integrally joined together and sealed in an air-tightmanner.-

It will thus be seen that the lower-limb assembly 5 comprisestwo'principal portions. One of these portions includes the exterior tube49, the fitting 52 and nut 53, the insulating plug 54, the stem 55 andthe sheath B and inner conductor HA of line H, all of these parts beingfixed with respect to one another. The other principal portion of thelower-limb assembly 5 comprises central sleeve 40 and enclosing tube 4|together with the discs 42 and 43 which unite the central sleeve andenclosing tube. The skirt portion 44 with its ring 45 and the condensercup 46 with its lock nut 41 may also be considered as included in thissecond portion of the lowerlimb assembly, although these parts are notactually fixed with respect to the enclosing tube and central sleevesince skirt 44 may be adjusted along the outside of the enclosing tubeand since condenser 46 may be screwed axially to adjust it along thecentral sleeve 40. It should be noted that in the completed beaconassembly the exterior tube portion of the lower-limb assembly 5 is fixedand the other portion of this assembly (including the central sleeve 40and enclosing tube 4|) is held in position by the frictional clamping ofthe lower end of exterior tube 49 against the enclosing tube 4|. Thus toadjust the overall length of the lower-limb assembly 5, it is merelynecessary to loosen the clamping screw extending through ears 56 andthen to bodily slide the enclosing tube and central sleeve portion ofthe lower-limb assembly up or down along the sheath B. When the correctadjustment of the length is attained thescrew extending through clampingears 50 may again be tightenedto fix the enclosing tube 4| and centralsleeve 40 in position.

Referring now more particularly to Fig. 6, the upper-limb assembly 6illustrated in this figure comprises a main tube 60 closed at one end bya brass disc 6| soldered to it. Into this brass disc 6| isthreaded thestem 55 which passes through the fitting 52 and is connected to theinner-conductor A of line H as previously mentioned. A spacer 56 isslipped over the stem 55 between disc El and insulating plug 54, so thatwhen the disc BI is screwed onto the stem 55 this spacer 56 will pressagainst the insulating plug 54 and thus further tend to maintain plug 56in Fig. 8 particularly well illustrates this portion of the structure.As shown in Fig. 6, inside of the upper end of the main tube 60 there isslidably fitted a telescopic extension tube 62 whose upper end is closedby a brass disc 53 soldered thereto. This extension tube 62 serves toadjust the length of the upper limb assembly 6 of the main dipole, andafter the proper adjustment has been obtained this extension tube 62 islocked in place by tightening a screw which passes through a pair ofclamping ears G5 similar to the clamping ears 50. The upper end of themain tube 60 is slotted so that by means of the clamping ears 65 thismain tube 60 is tightly clamped against the extension tube 62.

Referring now more particularly to Fig. 7, the auxiliary wavecontrolling assembly I illustrated in this figure, comprises anauxiliary enclosing tube 10 somewhat similar to the enclosing tube 4| ofassembly 5, this auxiliary enclosing tube 10 being adiustably attachedto the same central sleeve 40 to which enclosing tube 4| is fixed aspreviously mentioned. For the purpose of such adjustable attachment oftube I to the sleeve 40, this sleeve is threaded near its lower end anda brass disc H which is soldered to the lower end of auxiliary enclosingtube 10 is screwed onto this threaded lower end and secured in placeafter adjustment by lock nut 12. An insulating disc 13 is fixed insidethe auxiliary enclosing tube 10 near its upper end, and is adapted toslidably bear against the correspond ing portion of sleeve 40. Since itis preferable that the portion of sleeve 40 against which disc 13 slidesshould not be threaded and since in any case it is advantageous to beable to remove condenser cup 56 of assembly from the sleeve 60 withouthaving to screw it along the full length of this sleeve, it is preferredto make thesleeve 4t in two parts as shown in Fig. 7, and to unite theseparts by means of a coupler 74 which is preferably soldered to the lowerportion of sleeve to and into which the upper portion of sleeve 40 isscrewed. It will be understood, however, that sleeve 60 may also be madein one integral piece since the construction of this sleeve in two partsis merely a matter of manufacturing convenience and expediency.

Near the upper end of auxiliary enclosing tube a tubular skirt I5 isadjustably attached by set screws which pass. through a brass ring 16soldered to this skirt. Cooperating with tubular skirt l5 and withthe-upper end of auxiliary enclosing tube 10 is the auxiliary condensercup H which is threaded on sleeve 4|] and locked in position by nut 18.Preferably the total length of the auxiliary enclosing tube 1|] issomewhat longer than the length of enclosing tube 4| between its lowerend and the point at which disc 42 is attached. If this is so, thetubular skirt portion and condenser cup 11, or at least one of these,will preferably be somewhat shorter than the corresponding condenser,cup and tubular skirt 46 and 44 of assembly 5, since it is ordinarilydesired that the chamber enclosed by auxiliary enclosing tube Ill shouldbe resonant to approximately the same frequency as the chamber enclosedby enclosing tube 4| below disc 42.

The general manner in which the assemblies 5, 6 and I are combined witheach other and with other parts to constitute the main radiating dipoleI 0 can best be seen from Figs. 4 and'8. As

already explained in connection with the description of Figs. 5 and 7,and as is plainly evident from Fig. 4, the assemblies 5 and 1 are unitedby the common central sleeve 40' since both the auxiliary enclosing tubeIll and condenser cup 11 of assembly 1 as well as condenser cup ofassembly 5 are adjustabl'y attached to this common central sleeve, andsince the enclosing tube 4| of assembly 5 is fixedly attached tothis'same sleeve. It will thus be evident that upon adjustment of thelength of the lower-limb assembly 5 sliding enclosing tube 4| upward ordownward within the exterior tube 49, as previously described, thespacing between the adjacent ends 01. assemblies I and 'I will not bealtered and likewise the condenser adjustment of each of theseassemblies will not be altered. It will also be apparent that thecondenser adjustment of the auxiliary wave controlling assembly I may bevaried by screwing the enclosing tube 10 up or down along the centralsleeve 46 without varying the separation between the assemblies I and I.

As can best be seen from Fig. 8, the assemblies I and I are fixed withrespect to one another by the fitting II, the insulating plug I4 and thespacer II. The adjustment of enclosing tube 4| upward or downward withinthe exterior tube 46 for adjusting the total length of the lowerlimbassembly I will not in any way vary the separation between assemblies Iand I. Similarly the adjustment of telescopic extension tube 62 upwardor downward within the main tube 66 to vary the total length ofupper-limb assembly 6 will not in anyway alter the spacing between theupper-limb assembly and the lowerlimb assembly. These two assemblies 6and 6 are supported by clamp 66 attached to the end of insulators IIwhich are screwed to the housing 3!. This housing 3| is in turn fixed tothe cross arm l4 which, as previously explained, is attached to the polel3.

At the lower end of line II a suitable insulating and air-tight seal isprovided preferably similar to the seal at the top of this line, and ifdesired means may be provided for maintaining the interior of the tubefilled with an inert gas or with dry air or some other gas at normal orelevated pressure.

The exact construction of the preferred embodiment of my inventionhaving been fully described, the operation thereof may be briefly setforth. For a further disclosure of the principles of operation of theauxiliary wave controlling assembly I and the lower portion of the lowerlimb assembly I below disc 42, reference is made to the previouslymentioned application filed by Frederick A. Kolster, on or about April28, 1938', and assigned to the same assignee as the present application.

The toroidal chamber formed by the lower portion of enclosing tube 4|(below the disc 42) and the corresponding portion of central sleeve 46together with condenser cup 46, tubular skirt 44 and disc 42, constitutea toroidal resonating circuit which may be tuned by varying the capacitybetween condenser cup 46 and the coop-, crating portions of 44 and 4|.To so vary this capacity it is preferred to effect the coarseradjustment by loosening the set screws which fix skirt 44 to the tube4|, and then sliding this skirt up or down so as to attain approximatelythe correct tuning. A slight further adjustment may be conveniently madeto obtain exact tuning by loosening the lock nut 41 and screwing thecondenser cup 46 up or down by a small fraction of an inch, but it ispreferred to effect only the fine tuning in this latter manner since anyconsiderable displacement of condenser cup 46 would substantially varythe spacing between assembly I and assembly I, and such a variationmight require retuning of assembly I in case there were any appreciablestanding wave intensity along the sleeve 40 between the two assemblies.

Similarly the chamber formed by auxiliary enclosing tube 16 and thecorresponding portion of central sleeve 46 together with disc II and atthe other end of the chamber condenser cup TI and tubular skirt IIconstitute a second toroidal resonating circuit which is also tunable.To tune this auxiliary resonating circuit it is preferred to effect thecoarse adjustment by loosening-the set screws which fix skirt 'II to thetube II and then moving this skirt up or down along the tube II toobtain approximately the correct adjustment. The finer adjustments arepreferably effected by screwing the disc H and tube 16 up or down alongthe central sleeve 46 since such an adjustment will not vary the spacingbetween the assembly I and the assembly I.

By adjusting the tuning of the toroidal circuit of assembly I thepassage of waves through this circuit may be controlled in almost anydesired manner. If this resonant circuit is tuned approximately toresonance, a condition can be obtained in which in spite of the presenceof very high voltage waves along skirt 44 and the other externalportions of the assembly I which lie above this skirt, a very slight andin fact practically negligible wave intensity will exist on condensercup 46 and on all the other portions of the structure below thecondenser cup. Thus the I surface constituted by exterior tube 46, theexposed portion of enclosing tube 4! between the lower end of exteriortube 46 and the skirt 44. and finally the skirt 44 itself, may beconsidered as constituting the lower limb of the main radiating dipole,while all the portions of the structure below the lower end of skirt 44may be considered as practically ineffective so far as radiation isconcerned because of the fact that there is only a negligible intensityof waves in these remaining portions.

I have found, however, that the adjustment of the resonant circuit ofassembly 5 affects not only the degree of wave blocking or the amount ofattenuation of waves in passing from the effective radiation portion ofthe lower dipole limb to the portions of the structure therebelow, butalso at the same time influences the coefllcient of reflection of wavesfrom the lower end 01' the effective radiation portion of the lowerdipole limb. Since it is desired for symmetrical radiation to adjust theresonant circuit oi assembly I in such manner that the reflectioncoefiicient from the lower end of skirt 44 will closely simulate thereflection coeflicient from the upper end of the upper limb of thedipole (i. e. from the upper end of telescopic extension tube 62) I havein accordance with one feature of my invention provided the furtherauxiliary wave controlling assembly l disposed immediately below theassembly 6 and adapted to be independently adjusted for furthercontrolling any waves which may pass down below the lower end of skirt44.

According to the preferred method of adjusting the structure abovedescribed, the resonant circuit of assembly 5 is first tuned so as toprovide as high an attenuation of waves of the desired frequency aspossible. Then the two limbs of the dipole are adjusted to thedesired-preferably equal-lengths and the distribution of standing wavesalong the efi'ective radiation portion of assembly I which constitutesthe lower limb of the dipole is compared with the correspondingdistribution along the upper limb of the dipole constituted by assemblyI. The resonant circuit of assembly I is then finely adjusted so as tomake the two distributions as nearly symmetrical as possible. When thisis done, it may be found that the attenuation of the waves passing belowthe lower end of skirt 44 is not sufficient to render the waves belowthis point completely negligible. The resonant circuit of assembly I isthen adjusted so as to more completely extinguish the waves so as toprevent their passing down over the line H. In some cases suchadjustment of assembly 1 will slightly alter the distribution of wavesalong the lower limb of the dipole and in such case assembly 5 shouldagain be readjusted.

Ordinarily no more adjustment than this will be necessary, but incertain cases where a very accurate symmetry between the two halves ofthe dipole is required and at the same time a very complete extinctionof the waves passing down over the line I I is necessary, the distancebetween the assemblies 5 and I may be varied by screwing disc 1| downalong the central sleeve 40 and then screwing condenser cup 11 downalong this central sleeve 40 by a corresponding amount. A fineadjustment of the separation between the two assemblies 5 and I is notnecessary, and

EDI

therefore it is in all cases sumcient to try a very few difierentspacings, readjusting the assemblies Sand 1 each time to obtain therequired distribution on the lower limb of the dipole and at the sametime to obtain the maximum attenuation of waves passing down over thetwo assemblies 5 and 1.

It will be noted that the effective outer surface. of the lower limb ofthe dipole is very nearly a continuous smooth cylinder with nodiscontinuity except the very slight increase of diameter at ring 45.Furthermore, the diameters of the upper and lower limbs of the dipoleare substantially the same. These factors when combined with thepossibility of obtaining exactly the same reflection coeflicient at theends of the two limbs of the dipole, and at the same time of obtaining asubstantially complete extinguishment of waves passing down over theline H, enable a' very symmetrical radiation to be obtained. At the sametime, distortions of the radiation pattern with respect to anyhorizontal diagram taken in a plane perpendicular to the axis of thedipole, are eliminated'by the concentric arrangement of the feed-linewith respect to the.

dipole.

It should furthermore be noted that the small amount of waves which dopass down beyond the end of skirt 44 and are finally extinguished byassembly 1 are insuilicient to cause any significant distortion of thepattern since these waves are only effective over a distance of a fewinches. The positioning of assembly I with the condenser cup uppermostaids in reducing the effect of such weak attenuated waves which mayexist below the .lower edge of skirt 44 and above the lower edge ofcondenser cup 11. It should furthermore be noted that if it is desiredto take account of even these weak waves occurring in a very limitedregion, this can be done by suitably adjust.- ing the length of theupper dipole limb so as to slightly differ from the length of the lowerdipole limb, and then correspondingly adjusting the distribution ofwaves along the two limbs. Ordinarily, however, such adjustments are notat all necessary since the structure is inherently highly symmetricaland can be made to give an almost perfectly symmetrical radiationdiagram merely by tuning the two assemblies 5 and I and adjusting thelengths of the two limbs of the dipole so as to be equal.

It should be noted that if the slight discontinuity intoduced by ring 45is deemed objectionable, the condenser cup 46 may be arranged tocooperate with the inside surface of enclosing tube 4| rather than withthe outside surface thereof and the tubular skirt 44, if required atall, may then be located'inside of tube 4| instead of outside of it, sothat the outside surface of the lower dipole limb will be perfectlycylindrical. In practice, however, it is found that the very slightvariation in diameter introduced by the presence of spacing ring 45 andskirt 44 can. be neglected.

It should be noted that the positions of wires constituting lines 22 and23 are such that even without the presence of chokes 24 these wireswould introduce. substantially no distortions in the radiation patternsince they are at all points transverse to the field of the dipole. Itis preferred, however, to add the chokes 24 and the further chokeswithin the relay housings of relays and 2|, in order to prevent anypossible influence of the lines 22 and 23 upon the pattern if theselines are not at all points perfectly perpendicular to the field of theradiating system. Furthermore, at least one set of chokes in each lineis desirable in order to prevent the passage of the ultra-short wavesdirectly from the line I I over the lines 22 and 23, thus causingunnecessary losses and possible injury to the relays as well as perhapsa very slight radiation due to the physical separation of the two wiresof each of the lines 22 and 23. e

Although in the preferred embodiment of my invention above described andshown, the transmission line I l is of the coaxial type, this line mayalso be shielded two-wire line of a high frequency type. It may bepreferred to employ such a two-wire line with a'conducting sheath if thetransmitter station 12 has a balanced output, If such a shieldedtwo-wire line is employed, one wire may be connected to the limb B andthe other wire may be connected to the limb 5.

Although I have shown and described certain particular embodiments of myinvention for the purposes of illustration, it will be understood thatadaptations, modifications and alterations thereof occurring to oneskilled in the art may be made without departing from the scope of theinvention as defined in the appended claims.

What is claimed is:

1. A dipole antenna structure for producing symmetrical radiant actioncomprising a multiconductor transmission line having a conducting shieldconductor and at least one inner conductor, an elongated hollow radiatorencircling said shield conductor adjacent one end thereof, a secondradiator of similar external configuration extending coaxially with saidfirst radiator beyond the end of said shield conductor, the spacebetween the adjacent ends of said radiators being relatively small, aconnection between said shield conductor and one of said radiators andadditional connections between the adjacent ends of said radiators andthe conductors of said line.

2. A dipole antenna structure for producing symmetrical radiant actioncomprising a coaxial transmission line having a center conductor and thesheath thereof and forming a sleeve encircling said sheath, a secondradiator of similar external configurationattached to said centerconductor and extending in the opposite direction to said radiator firstmentioned, the space between the adjacent ends of said radiators beingrelatively small and an additional connection from said sheath to apoint intermediate the ends of said first mentioned radiator.

4. A dipole antenna array comprising a coaxial tr as on line having acenter conductor and an outer conducting sheath, an elongated hollowradiator connected to the end of said sheath and forming a sleeveencirclingsaid sheath, a second radiator attached to said centerconductor and extending beyond the end of said sheath coaxially withsaid first radiator, a second dipole including two conductor membersdisposed end to end parallel to said first dipole and spaced therefromto influence the radiation pattern of said dipole, a keying relaypositioned adjacent the inner ends of the conductor members forming saidsecond dipole for altering the eflect of said second dipole, andconnections from the sheath and inner conductor of saidlinefirstmentionedtosaidkeyingrelamsdd connections extending at ri htangles to the axis of said first dipole and from a point adjacent saidend of said sheath.

5. A dipole antenna structure for producing symmetrical radiant action,comprising a coaxial transmission line having a center conductor and anouter conducting sheath, a first radiator including a resonant circuitcomprising a sleeve encircling said sheath adjacent the end thereof,said sleeve and sheath extending in overlapping, spaced, concentricrelation, anda second radiator connected to said center conductor andhaving substantially the same external configuration as said sleeve. 1

8. A dipole antenna structure for producing symmetrical radiant action,comprising a multiconductor tron line having a conductive shield, aresonant circuit comprising a sleeve encircling said shield adjacent oneend thereof and a member in capacitive relation therewith, said sleeveand member forming a first radiator, a second radiator of an externalconfiguration similar to that of said sleeve extending beyond saidshield coaxiallywith said sleeve and connections from each of saidradiators to separate conductors of said transmission line.

JOACHIM GOLDMANN.

